The present invention relates to die attach methods and integrated circuit (IC) devices.
During the manufacture of IC devices, a plurality of IC chips, also known as a "die", are bonded to the paddles of a lead frame. A die 10, bonded to a paddle 12 of lead frame 14 is shown schematically in FIG. 1. This step is commonly referred to as "die attach". Following die attach, electrical connections are established between each die 10 and the fingers 16 of the lead frame with wires 18 by a wire bonding process. Finally, each die is enclosed in an individual package and the packages are separated to form individual IC devices.
The die is typically bonded to the lead frame using an electrically conductive, e.g., silver filled, die attach adhesive. Generally, dots of the die attach adhesive are applied to the lead frame paddle by a pneumatically energized syringe. Die attach adhesives applied in this manner generally include significant amounts of volatile solvent to reduce their viscosity sufficiently to allow the adhesive to be pumped through the syringe. It is also generally necessary that the solvent have a low evaporation rate, to provide a long working time to prevent the adhesive from drying out during the die attach process.
Several disadvantages tend to result from applying the die attach adhesive by syringe. First, it is often difficult to control both the amount of adhesive dispensed and the bond line thickness (thickness of adhesive under the die). If too much of the adhesive is applied, adhesive may run up the sides of the die, potentially causing short circuiting and/or wire bonding problems. If too little adhesive is applied, the bond line thickness may be insufficient, resulting in poor bond strength. Second, the solvents used to reduce the adhesive viscosity and provide working time may outgas, resulting in actual or perceived reliability problems. Finally, air may be trapped under the die, creating voids which can weaken the bond strength and interfere with heat transfer between the die and the lead frame paddle.